Functional mitral regurgitation (MR) is a common complication of ischemic heart disease. Two large clinical trials confmned an adverse effect of functional MR on survival after a heart attack. However, studies in heart failure are small and mainly limited to patients with nonischemic cardiomyopathy. Recent animal studies have challenged the traditional concept that functional MR is a consequence of mitral annular dilation, instead suggesting that functional MR is due to leaflet tethering by outward expansion of the left ventricular wall (i.e. LV remodeling). This has critical implications regarding the correct surgical approach to correcting functional MR. To date, no large prospective studies have examined the mechanism(s) of functional MR in ischemic cardiomyopathy, nor has the interaction between mechanism and prognosis been explored. This is a crucial knowledge gap because 1) 70% of heart failure cases are caused by ischemic heart disease, and 2) functional MR occurs in around 60% of patients with ischemic cardiomyopathy. This proposal aims to fill these gaps by defining the mechanism(s) of functional MR by transesophageal echocardiography in a large clinical trial of patients with ischemic cardiomyopathy. The following specific aims will be addressed: Aim 1: To define the mechanism(s) of functional MR in isehemie cardiomyopathy Aim 2: To define the effect of therapy on mechanism and severity of functional MR Aim 3: To evaluate the effect of functional MR on prognosis is ischemic cardiomyopathy Aim 4: To evaluate the effect of myocardial viability on functional MR and its response to treatment. We propose to accomplish these aims as an ancillary study to the Surgical Treatment for Ischemic Heart Failure (STICH) Trial. The STICH Trial will compare surgical revaseularization versus medical therapy for treatment of heart failure in 2800 patients with ischemic cardiomyopathy, and therefore affords a unique opportunity to investigate the mechanism(s) of functional MR. Despite its known clinical utility for assessing the mechanism and severity of MR, TEE is not currently included in STICH.